Changing partition type uses 100% cpu for long time

Binary package hint: udisks

In the Administration -> Disk Utility I went to my HD under SATA Host Adaptor -> 320 GB Hard Disk. Selected an "Unknown" 48GB partition within the extended partition. Clicked Edit Partition, changed the type to 0x07 NTFS and clicked Apply. Wait cursor appeared and CPU went to 100% utilisation. Continued for 7+ minutes before eventually terminating and NOT making the type change!

Line from ps aux:
root 2814 83.8 0.0 3744 1388 ? R 15:00 7:13 udisks-helper-modify-partition /dev/sda 272152657920 47919923200 0x07

May be HD problem as cfdisk /dev/sda gives error even though whole thing was created by Ubuntu installer:
FATAL ERROR: Bad primary partition 1: Partition ends in the final partial cylinder

Regards,
Andrew

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: udisks 1.0.1+git20100614-2
ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic i686
NonfreeKernelModules: nvidia
Architecture: i386
CustomUdevRuleFiles: 10-vboxdrv.rules
Date: Sun Sep 26 15:12:56 2010
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Beta i386 (20100901.1)
MachineType: Dell Inc. XPS M1530
ProcCmdLine: BOOT_IMAGE=/vmlinuz-2.6.35-22-generic root=UUID=6ccfb739-7285-4884-b91c-6722012bb1e3 ro quiet splash
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.utf8
 SHELL=/bin/bash
SourcePackage: udisks
dmi.bios.date: 03/19/2008
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A08
dmi.board.name: 0D501F
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA08:bd03/19/2008:svnDellInc.:pnXPSM1530:pvr:rvnDellInc.:rn0D501F:rvr:cvnDellInc.:ct8:cvr:
dmi.product.name: XPS M1530
dmi.sys.vendor: Dell Inc.